A tendon is a soft, dense, regularly arranged connective tissue that attaches muscle to bone and is important for extremity function. Tendons are comprised of mostly type I collagen (80% by weight) that are arranged in fibrils. The fibrils form multiple fascicles within each tendon, which includes the basic tendon fibril and also fibroblasts in parallel rows. Covering the tendon is a thin fascia membrane called the epitenon layer. Tendons also contain some elastin fibers, a proteoglycan matrix, and proteinaceous filler between the connective tissue fibers.
When tendons are lacerated or rupture, they demonstrate poor spontaneous regenerative capabilities and complete regeneration is almost never achieved despite intensive remodeling. Because tendons are required to glide, they rely on their smooth fascial membrane sheath to cover the tendon while also allowing it to move and slide freely along adjacent tissue structures such as muscle, skin, narrow fibrous tunnels, other tendons, or bone. They are also simultaneously relied upon to resist tremendous forces acting upon them, and each tendon relies upon the strong fibril network to maintain its strength.
Patients whose tendon(s) are in discontinuity experience pain, reduced mobility, and overall decrease in function. End-to-end or end-to-side repair techniques can be useful in reattaching or reconstructing injured tendons. However, the timing of when to perform the repair and when to initiate the post-operative rehabilitation remains controversial. If the tendon repair is performed too late following the injury, the tendon edges may retract too far apart and a primary repair may not be able to be accomplished, and a tendon graft may be required. If the repair is performed in a timely manner, usually within seven to ten days, but the tendon rehabilitation is initiated too aggressively, gapping at the repair site or even early rupture of the repair site may occur. This is the result of initial weakness at the repair site due to the suture-repair technique for tendon repair. However, if rehabilitation is delayed in order to allow for the tendon to heal, then scarring and adhesions may form in the tendon sheath. This may result in decreased range of motion and, ultimately, poor function. In addition, because of the tight space within the tendon sheath, there is little room for scar tissue, suture, or additional apparatuses to hold the tendons together. Any additional bulk will decrease the gliding function of the tendon and lead to decreased range of motion, stiffness, and possible risk of rupture. This is present in all current treatments of tendon repairs, which include suture-based repairs.